COMPARISON OF THE SUPPRESSIVE EFFECT OF 2 DOSES (500 MG VS 1500 MG) OF ORAL CALCIUM ON PARATHYROID-HORMONE SECRETION AND ON URINARY CYCLIC-AMP

The respective effects of the ingestion of two different doses of calc ium (500 and 1500 mg) on serum ionized calcium, intact parathyroid hor mone (PTH 1-84), and the urinary excretion of 3',5'-cyclic adenosine m onophosphate (cyclic AMP) were evaluated in 15 young male adults. Ioni zed serum calcium and PTH 1-84 were measured before and 1 hour, 2 hour s and 3 hours (P1, P2, and P3) after the oral intake of calcium. Cycli c AMP was measured in 2-hour urine samples collected before and during 4 hours after the ingestion of calcium. Similar increments in serum i onized calcium (DELTACa2+) were observed except at P3 where the DELTAC a2+ was significantly (P < 0.02) higher after 1500 mg (0.088 mmol/lite r) than after 500 mg of (0.062 mmol/liter). In the same way, the compa rison of the PTH 1-84 concentrations showed no statistical difference except at P3 (P < 0.002). When expressed as a percentage of P0, the P1 and P2 PTH 1-84 values were more suppressed after 1500 mg than after 500 mg of calcium (P1: -69% vs -59%; P < 0.02; P2: -66% vs -50%; P < 0 .02). However, the simultaneous cyclic AMP responses (-24% vs -19%) we re not significantly different. The results show that the respective m aximal effects on PTH secretion and on urinary cyclic AMP of two very different oral doses of calcium are only slightly different.